Ultrasound imaging of the lateral abdominal wall muscles in individuals with lumbopelvic pain and signs of concurrent hypocapnia

The purpose of this study was to compare the change in thickness of transversus abdominis (TrA) and internal oblique (IO) muscles, during resting supine respiration, in individuals with lumbopelvic pain (LP) to those who in addition to LP, demonstrate signs of concurrent hypocapnia (LP&HYPO). B-mode ultrasound images were obtained at the height of inspiration, and at the end of expiration, over three subsequent breaths during a single session. The average percent change in thickness of TrA during resting respiration in the LP&HYPO group (20.8±7.6%) was found to be statistically greater (P<0.001) than that of the LP only group (1.3±5.8%), while the difference between the groups for the percent change in thickness of IO (LP&HYPO 9.2±8.1%, LP 2.0±7.2%) did not differ (P=0.073). These findings suggest that respiratory modulation of TrA thickness, as measured by ultrasound imaging, greater than 20%, detected in a resting supine position, may be associated with an episode of hypocapnia, and if present warrants further investigation.